Calculate the ratio of the drag force on a jet flying
Answers
Answer:
Drag force
D
experienced a flying object depends on the density of the air; square of the velocity of the object; viscosity and compressibility of surrounding air; the size and shape of the object, and inclination to the air flow of the object.
One way to deal with complex dependencies is to characterize the dependence by a single variable. For drag, this variable is called the the drag coefficient, and designated
C
d
. This allows us to collect all the effects, simple and complex, into a single equation. The drag equation states that drag
D
is equal to
C
d
times the density
ρ
of surrounding air times half of the velocity
V
squared times the reference area
A
r
.
Basic drag equation is written as
D
=
C
d
⋅
A
r
⋅
ρ
V
2
2
∴
The required ratio is
D
j
D
p
=
(
C
d
⋅
A
r
⋅
ρ
V
2
2
)
j
(
C
d
⋅
A
r
⋅
ρ
V
2
2
)
p
where subscript
j
is for jet and
p
for plane.
It is given that that the jet and the airplanes have the same effective cross-sectional area and drag coefficient.
Above equation becomes
D
j
D
p
=
(
ρ
V
2
)
j
(
ρ
V
2
)
p
Inserting given values we get
D
j
D
p
=
0.45
(
753
)
2
0.70
(
753
2
)
2
D
j
D
p
=
4
×
0.45
0.70
=
2.57
Explanation: